The present invention concerns the administration by injection to patients of liquid compositions for therapeutic or diagnostic purposes. It more particularly concerns a power assisted method and device for controllably dispensing a liquid medicament or diagnostically active contrast agent, the homogeneity of which is preserved throughout delivery. Typically, the contrast agent is an aqueous suspension of gas filled microvesicles, namely microbubbles bounded by a surfactant stabilized gas/liquid interface, or microballoons bounded by a tangible material envelope.
Power injectors and mechanically assisted infusion systems for controllably dispensing therapeutically active medications are well known in the art. Typically, such devices include an automatic injector for syringes containing an injectable liquid and a plunger or piston movable within the barrel of the syringe to expel said liquid through a tip thereof and injecting into a patient via a tubing connected to an injecting needle or catheter. For controlling the injections parameters, the plunger is driven by means of an electromechanical arrangement organised to push the plunger at a desired rate, continuously or at chosen intervals, so that the amount of medication is delivered to the patient""s body under strictly determined conditions. For instance, in the case of intravenous dispensing contrast agent formulations for diagnostic purposes (X-ray, MRI or ultrasound), the rate and the mode of injection can be accurately controlled to match the requirements of the imaging methods and detector systems used to investigate the circulation or a specific organ in the body. Typical automated injection devices are illustrated and described in U.S. Pat. No. 5,176,646 incorporated herein by reference.
Although the automated injectors known are highly sophisticated instruments capable of mastering most injection problems experienced in practice, there remains at least one variable factor not yet under control. Indeed the known power injectors have no control of the homogeneity of the liquid stored within the syringe barrel during the course of its application. This kind of problem is of course non-existent with xe2x80x9ctrue solutionsxe2x80x9d (i.e. solutions to the molecular level) since in this case no concentration change can occur in the course of time; it however may become important when the injectable formulation is a suspension or dispersion of active particles which tend to settle, coalesce or segregate with time in the syringe. Indeed, even some modest separation of the particles by gravity or otherwise from the carrier liquid in the course of administration of the formulation may have very important influence on reproducibility and reliability of the tests. Hence, in this case, a method and means to keep the syringe content homogeneous during injection is highly desirable. The present method and device constitute a very effective solution to the aforediscussed problem.
Briefly stated, in order to secure homogeneity of a liquid suspension of particles within the barrel of an injector device, the invention provides a method and means whereby the particles are kept under sufficient agitation so as not to settle, segregate or agglomerate in the carrier liquid. This may involve acting on the carrier liquid itself, i.e. on the bulk of the suspension, or may involve acting only on the particles (in this case, one would expect the moving particles to impart motion to the carrier liquid by viscous friction). The agitation means may be provided within the syringe or in some cases outside thereof; for instance with magnetic particles, the particles can be subjected to an external variable magnetic field, the oscillation or rotation of which will set them into motion, the moving particles then acting on the carrier liquid and keeping the suspension homogeneous.
In the case of particles not sensitive to external fields, mechanical agitation is provided to the extent that it is sufficient to keep the suspension homogeneous but insufficient to break or damage the particles or disturb their distribution. For this, the syringe barrel may be subjected to motion, said motion being continuous or discontinuous, regular or irregular; the motion can possibly have a shaking, rocking or oscillating effect on the syringe. The frequency, intensity and rate of the motion is such that it will not interfere with the control of delivery parameters of the suspension.
The embodiments disclosed below in connection with the annexed drawings provides very effective means to keep the syringe content under sufficient agitation to secure injection of a homogeneous therapeutic or diagnostic liquid compositions into a patient.